1. Field of the Invention
This invention relates to a tire inflation apparatus and method, and, more particularly, to such a method in which pneumatic tires are first evacuated via a vacuum pump and then inflated with a purified, dried gas under pressure, such as pressurized nitrogen without allowing any ambient air to reenter the evacuated tire.
2. Description of the Related Art
Pneumatic tires for automobiles, aircraft and other vehicles have traditionally been inflated by compressed ambient air. Compressed air works generally well with bicycle tires, tractor tires and even standard automobile tires run at relatively low speeds where exacting tire balance and consistent tire pressure is not critical. In the case of uses such as race cars, dragsters, and high altitude aircraft, compressed ambient air is not a satisfactory medium for inflating tires for a variety of reasons. When compressed air is introduced into a tire via a compressor open to the ambient atmosphere, water vapor and other impurities are introduced into the tire in the same proportions as they occur in the ambient air. With all of the moisture and other impurities present, air volume in the tire fluctuates fairly widely with temperature, particularly due to the moisture changing from liquid to vapor form and vice-versa as temperatures in the tire change. As a rule of thumb, the pressure of the air in tires inflated with compressed ambient air will change about 1 psi for every 10 degree Fahrenheit change in temperature. Thus, a tire inflated at 60 degrees Fahrenheit will be substantially under inflated at 20 degrees due to the combined effects of temperature in reducing gas pressure and moisture condensing out of the air within the tire. Conversely, as temperatures increase to 90 degrees Fahrenheit, the tire will be substantially overinflated due to the water being vaporized and the attendant increase in air pressure due to temperature. These under or over inflation conditions can adversely affect rolling friction of tires on pavement, thus decreasing gas mileage. Tire wear is also substantially increased when tires are not inflated to the manufacturer's recommendations. Water vapor within tires can also induce rust within steel belted radials, which further reduces tire life. Furthermore water vapor introduced into a tire in a high altitude jet airplane, for example, will condense and then freeze and form ice crystals which generally fall to the bottom of the tire as it lies stationary in the wheel well of the airplane. When the airplane lands, the ice crystals can create a substantial imbalance in the tire, which must accelerate virtually instantly from rest to 150 or more miles per hour. As the tire accelerates, the ice crystals are thrown around the rolling tire by centrifugal force, leading to further imbalance, increasing internal wear, and also increasing the likelihood of tire blow-outs. In the case of race cars and dragsters, since the water vapor introduced into the tire condensed and vaporizes at unpredictable times, condensed water within the tire lags behind the column of air within the tire as the tire is rapidly accelerated. It is believed by the inventor that this is the cause of much of the "tire chatter" which is such a problem in dragsters and other racing cars, as water within the tire drags relative to the tire rotation, the tire becomes unevenly pressurized around its perimeter, thus inducing up and down movement or chatter. Furthermore, as the race car tires spin at high speed, considerable heat builds up in the tires themselves thus considerably increasing the internal tire pressure due to the expansion of the water vapor.
In order to eliminate these problems, race car owners, space shuttle transport vehicles, earthmoving and mining equipment and commercial and military high altitude aircraft often inflate their tires with compressed nitrogen or other generally unreactive and non-combustible gasses such as argon or sulfur hexafluoride. Nitrogen is an ideal gas for such a purpose since it is chemically unreactive, non-combustible, non-flammable and non-corrosive, and, when dry, is relatively stable in volume through a wide range of temperatures. For example, the specific volume of a quantity of dry nitrogen gas at 1 atmosphere of pressure varies less than 13% in a range of -10 degrees F. to +116 degrees F. Thus, the use of nitrogen to inflate a pneumatic tire offers a large reduction in fluctuations of internal tire pressure due to temperature variations over those which occur when moisture laden compressed ambient air is used. Furthermore, since nitrogen is stored in pressurized tanks under controlled conditions, the nitrogen gas can be dried and purified as it is placed into the tank, thus minimizing moisture and other impurities transferred into the tire.
However, when new or repaired tires are first placed on a wheel, they must be inflated under high pressure to get the tire bead to seat on the wheel rim. In order to accomplish this, even in race car and high altitude aircraft tires, compressed ambient air is used. Once the tire is inflated and properly seated on the wheel rim, the compressed air is bled off via the tire's Schrader spring loaded valve and a source of compressed nitrogen is then attached to the tire valve and the tire is reinflated. With this method, the tire's internal pressure is simply returned to ambient pressure before being filled with nitrogen. This leaves a quantity of air at ambient pressure in the tire which air quantity, at ambient pressure, is equal to the internal volume of the tire. Along with the quantity of air left in the tire, moisture and other gaseous impurities are present in the tire in the same proportion as they are found in the ambient atmosphere. When the dry, purified nitrogen is introduced into the tire under pressure, it mixes with the air, moisture and other impurities already present in the tire as the tire is being inflated. The inflated tire is thus filled with a quantity of air including attendant moisture and other impurities and a larger quantity of nitrogen, thus repeating, albeit at a reduced level, the problems associated with the use of ambient compressed air.
It is clear, then that a need exists for a tire inflation apparatus and method which avoids these problems of the prior art. Such a tire inflation apparatus should preferably inflate tires with compressed, purified and dried gas, such as nitrogen, to the manufacturer's recommended tire pressure while minimizing or eliminating moisture and other impurities in the tire.